Field of the Disclosure
The present disclosure relates generally to a method and composition for reducing hydrate formation and more particularly to reducing hydrate formation using organic salts.
Description of the Related Art
After construction and deployment of pipelines, manifolds, and stations (generally referred to herein as pipelines and pipeline systems), water is typically present within the pipelines from cleaning, flooding, hydrotesting, and/or other pre-commissioning operations. Hydrotesting typically includes filling a pipeline system with water and pressurizing the water to verify the integrity of the pipeline system.
The presence of bulk and/or residual water is a normal result of such pre-commissioning activities. After pre-commissioning activities are completed, remaining water is commonly removed from the pipelines prior to commencing service to avoid formation of hydrates, which can result from interactions between water and production fluids. For example, if natural gas is pumped through a pipeline that has water in it, under certain conditions the methane, isobutane, and/or other various components in the natural gas may interact with the water to form hydrates within the pipeline. Generally, colder ambient temperatures, such as those found within subsea pipeline systems, may promote hydrate formation. Such hydrates may partially or completely block the flow of production fluid through pipeline systems. Hydrate remediation or removal can be time-consuming and expensive.
One method that has been commonly used to mitigate hydrate formation includes removing bulk water in the pipeline by pushing one or more pipeline pigs down the pipeline. Pipeline pigs displace bulk water from the pipelines, but may leave residual water on the inside surfaces of the pipeline. Even residual water may result in the formation of hydrates in pipeline systems.
One known method employed to remove residual water from pipelines comprises using vacuum pumps to evaporate the water. The vacuum pumps lower the air pressure within the pipeline to below the vapor pressure of water at the ambient temperature, which causes the water to evaporate and allows for removal of the water vapor from the pipeline.
One known method of hydrate prevention includes pumping various solutions known to inhibit hydrate formation into a pipeline. Known hydrate-inhibiting solutions include formate salt solutions, methanol, and ethylene glycol. U.S. Patent Application Publication No. 2008/0314124 to Sweeny et al., titled “Composition and Method for Pipeline Conditioning & Freezing Point Suppression,” which is fully incorporated herein by reference, describes the use of aqueous metal ion formate salt compositions, such as potassium formate, as hydrate inhibitors. Hydrate-inhibiting solutions may be added to a pipeline system after a pipeline pig has removed bulk water from the pipeline system. Such solutions act to depress the freezing point of hydrates thereby reducing the formation thereof. Alternatively, the hydrate-inhibiting solution may be added to the water used to hydrotest the pipeline as a conditioner to prevent hydrate formation.
Another method to remove bulk and/or residual water from pipelines includes passing a series of pipeline pigs, alternating with slugs of a hydrate-inhibiting solution, through the pipelines. Using multiple, separated slugs of the solution produces a dilution effect on the relative residual water concentration, thereby leaving any residual liquid with a relatively high concentration of the hydrate-inhibiting solution.
Each of the foregoing methods has drawbacks. The use of vacuum pumps involves expensive equipment and may take considerable amounts of time to lower the air pressure within the pipeline to below the specified point. Handling and disposal of methanol, which is a flammable material, increases costs. Ethylene glycol is likewise expensive to handle and dispose of due to its toxicity.
The use of potassium formate as a hydrate inhibitor may also present several undesirable results. For example, potassium formate may be relatively expensive. Additionally, potassium formate may be corrosive to pipeline systems. As a further drawback, potassium formate has relatively low solubility at temperatures typically found in subsea pipeline systems, and in certain cases, over-land pipeline systems.
The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the drawbacks set forth above.